This invention relates generally to atomic or molecular beam devices using magnetically state selected or polarized atoms or molecules and more particularly to improvements in atomic beam frequency and time standards such as the atomic hydrogen maser, or the atomic cesium beam tube.
Many atoms or molecules in several of their quantum energy states have a magnetic dipole moment, or may have a magnetic dipole moment induced in the presence of an external magnetic field, and when present in a region where gradients in the external magnetic field also exist they experience forces which depend on the magnitude and sign of the magnetic dipole moment, and upon the magnitude and direction of the magnetic field gradient.
Magnetic state selectors, also known as focussing magnets, are devices through which a beam of atoms or molecules is made to pass, and in which atoms if different quantum energy states are selected, or focussed, or defocussed, so that the emergent beam is sorted out spatially, and atoms in one or more particular states (or polarizations) may be used in devices whose operation depends upon the presence or absence of one of more states.
For example, the atomic hydrogen maser is a precision frequency and time standard the frequency of which is derived from transitions between magnetic quantum energy states in the ground electronic state of atomic hydrogen. In the hydrogen maser, hydrogen molecules are separated into atoms in a gaseous radio frequency (RF) discharge, called the source, from which they emerge through a small tubular exit hole in a beam directed generally along an axis. A portion of the beam passes through a magnetic state selector placed along the axis wherein atoms in two of the four equally populated magnetic quantum states are caused to diverge from the beam (or become defocussed) and atoms in the other two states are caused to converge towards the axis. Thus a state selected beam of atoms is caused to enter a storage vessel within an RF cavity interaction region downstream of the state selector magnet wherein maser action takes place, and an RF signal is generated at the frequency of 1,420,405,751.6893 Hz or thereabouts. Through electronic circuitry this signa is used to generate standard frequency and time output signals.
State selectors used in the past have been difficult to construct and generally larger and heavier than theoretically required for the particular application because the precision of the bore and the gap dimensions was affected by the accumulated imprecision of the several parts. The lack of convenient facility for adjustment of the bore or gaps after the state selector is assembled makes use of the optimum geometrical configuration impossible or extremely difficult to achieve with the present state of the art.